list conversion question

Andrew Dalke adalke at mindspring.com
Sat Sep 4 06:27:58 CEST 2004


Paul McGuire wrote:
> Assuming im.histogram() returns a list like [ 0, 1, 0, 5, 43, etc. ] how
> about:
> 
> hist = [ 0, 1, 0, 5, 43 ]
> values = [ i for i in enumerate(hist)]
> values.sort(lambda a,b: cmp(b[1],a[1]))
> indexes = [ a for a,b in values ]

or tweaked a bit for speed (a sort with a lambda is expensive)
and for clarity, IMO,

pairs = [(value, offset) for (offset, value) in enumerate(hist)]
pairs.sort()
indexes = [offset for (value, offset) in pairs]

In Python2.4 this is allowed

 >>> hist = [ 0, 1, 0, 5, 43 ]
 >>> [pair[0] for pair in sorted(enumerate(hist),
...                             key=lambda pair: pair[1])]
[0, 2, 1, 3, 4]
 >>>

Not yet sure that that's a good thing.

				Andrew
				dalke at dalkescientific.com



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